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Journal of Scientific & Industrial Research
Vol. 63, April 2004, pp 365-375
Advances in the applied chemistry of allylic polymers
C C Menon*
Devi Nivas, Edathil Road, Tellicherry 670 101
and
A Selvaraj
Hindustan Aeronautics Ltd, Bangalore
Received: 21 May 2003; revised received: 22 December 2003; accepted: 30 January 2004
Investigation of diallyl phthalate polymer (DAPP) based moulding powder with partial substitution of DAPP by
epoxidisied DAPP polymer (EDAPP) indicates improvement in mechanical properties without detriment to electrical
strength. Peak performance is manifested at 20 per cent substitution. EDAPP is also found to be an effective reactive diluent
for cold setting epoxy resin adhesives. Bond strength is observed to be unaffected by extension up to 40 per cent. Hardboard
(Fibre board) modified by DAPP as an impregnant results in a novel wood-polymer composite with tangible improvement
of density, electrical strength, modulus of rupture and reduced water absorption having varied applications.
Keywords: Diallyl phthalate polymer, Epoxy resin adhesive, Bond strength
IPC Code: Int. Cl.7: B 27 K 3/08, C 01 B1 13/18
Introduction
Allylic polymers constitute an obscure segment of the mammoth polymer industry. Though derived from C-3
building block with associated cost advantages the special features of allylic polymerisation erode the benefits
accruing from raw material. The industrial precursors to allylic polymers like, allyl alcohol, allyl acetate, and
allyl chloride are difficult to polymerise1. Further, unlike vinyl polymerization allylic compounds polymerise to
generate only dimers, trimers, tetramers, and other cyclised low molecular weight material2. Perforce conversion
has to be restricted to 25 per cent to avoid the danger of catastrophic gelation3. Improvement in the economics
of the process by recovery and recycling of unreacted monomer is hampered by constraints imposed by
considerations of safety and hazards. Notwithstanding all these inconvenient features allylic polymers have
etched a niche for themselves as a “speciality polymer” in electrical and electronic applications.
Allylic polymers are generally derived from diallyl or triallyl compounds. These multifunctional monomers
have enabled the development of sophisticated products like, UV - curable printing inks for high speed printing
operations, and products for inclusion in composites which require high energy electron beam activation to
penetrate bulky objects.
Diethylene glycol bis-(allyl) carbonate is used to cast ophthalmic lenses and is called optical monomer4.
Diallyl phthalate polymer based moulding powders have acquired importance in electrical and electronic
sectors.
Moulding powders obtained by blending DAP polymer with lubricant,pigment catalyst, fillers, and mould
release agents have acquired importance for making components with multiple metallic inserts made of gold,
silver, copper, and alloys . The moulded products are utilised in wide range of applications like, sockets, TV
tuners, connectors, AC switch gears, rotary switches, aviation and space control panels. Rapid production of
shapes of outstanding dimensional stability with retention of electrical properties is possible. Prolonged service
at high humidity and temperature without any deterioration is another characteristic of the product. Defence
applications encompass aircraft and guided missile parts, radomes, and submarine applications.
The main hurdle to the expansion of the market is the
high cost. It was therefore envisaged that the ——————
*Author for correspondence
J SCI IND RES VOL 63 APRIL 2004
366
development of an extender-cum-builder for the polymer may contribute to market expansion and cost
reduction. Investigation of the suitability of epoxidised DAP monomer and polymer was therefore undertaken.
It was also believed that the epoxidised derivatives may acquire a foothold in the sphere of large volume
plastics like, PVC as plasticiser-cum-stabilizer. Another prospective outlet envisioned was as reactive diluent
for epoxy resins having a large consumption in the adhesive sector. Based on these tenets a project was
conceived with the salient features5 described subsequently:
(i) Study of the variation of the properties of DAP moulding powder as a function of the concentration of
epoxidised additive and the identification of the optimal concentration of the candidate product for peak
performance.
(ii) Evaluation of the performance of epoxidised DAP derivatives as reactive diluent for epoxy resin
adhesives and the identification of optimal dilution level.
(iii) Investigation of the potential of DAP polymer as an impregnant to wood to develop novel wood-polymer
composites.
Materials and Methods
(a) Diallyl Phthalate Polymer (DAPP) as well as moulding powder derived (WIPON) were obtained from
Western India Plywoods Ltd., Kannur.
(b) All other ingredients involved in the formation of moulding powder like glass fibre, magnesium and
titanium oxides, blue pigment, calcium stearates and tertiary butyl per benzoate were obtained from the
production wing of Western India Plywoods Ltd, Kannur.
(c) Epoxidised DAP monomer and epoxidised polymer (EDAPP) were obtained from Sri Ram Institute for
Industrial Research, Delhi from their pilot plant where a project sponsored by Western India Plywoods was in
progress. Epoxidised products had the under mentioned quality parameters.
Product Oxirane oxygen
value
Iodine
value
Epoxidised DAP
monomer
5.5 97
Epoxidised DAP polymer 1 28
Moulding powder was made by blending the required ingredients. Moulding was done in compression
moulding machine supplied by Nuchem, Mumbai Mouldings were done at 1500
C, pressure 15 kg/cm2, and
cycles of 3-5 min.
Mechanical properties were determined using Universal Testing Machines 2 and 20 t capacity.
Bar mouldings weighing 20 g and disc moulding of 60 g were made. Impact strength was determined using
Charpy FIE-IT-042 Impact Tester as per MIL-1071 procedure. Rockwell hardness was determined using Brunel
FIE/74/180 tester as per MIL-108 procedure.
Electrical resistivity of disc samples was determined using AE High voltage (150 KV) Tester supplied by
Automatic Electrical Ltd., Mumbai according to MIL-4031 procedure.
The rheological properties of the moulding composition were evaluated using Haake Rheocord – 90,
Computerised Torque Rheometer providing information relating to fusion rates, curing, shear heat stability,
torque, melt temperature, melt flow, and rotor speed.
Molecular weight distributions of DAP polymer and EDAP polymer were obtained by using Gel permeation
chromatograph supplied by Waters Inc, USA.
Araldite resin AW106
Hardner HY 953U
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
367
Manufactured and marketed by Hindustan Ciba – Geigy Ltd.
EDAPP polymer, 25 per cent, was allowed to swell in EDAP monomer (75 per cent) to obtain a
homogeneous viscous system. The viscous paste was used in different proportions with Araldite resin. The
variation of pot life and curing time of the composite adhesive at different concentrations were studied.
Different substrate configurations like, wood-wood, metal-metal, ceramic-ceramic, and ceramic-metal were
studied. Shear strength was determined by 2 t UTM machine.
The suitability of the composite adhesive for preparation of wood based laminate was studied. The face and
core veneers were Kalpine (Gurjan). Adhesive was spread on core veneer. The laminates were assembled and
configuration kept under pressure for 24 h. Glue shear strength was determined, using UTM as per IS 1708.
Pot life was determined by noting the time required for the composite adhesive to lose fluidity.
Cure time was indicated by the time required to reach the condition of the absence of tackiness on touching.
Standard hardboard having the following characteristics was used viz.
Density : 0.8 g/cc
Water absorption in 24 h : ≤ 40 per cent
Modulus of rupture : - 300 kg/cm2
DAP polymer of the
undermentioned quality was used
:
Softening range: 70 – 110o C
Acid value : 450
Iodine value : 55-65
Solubility in acetone : Good
Both the items were obtained from Western India Plywoods Ltd, Kannur. Acetone available commercially
was used.
Immersion of hardboard in a 10 per cent solution of DAP polymer in acetone containing 1per cent t-butyl
perbenzoate was the adopted procedure. Samples were taken to determine the progress of polymer absorption.
When the absorptions have reached the saturation level, the board was dried at 150oC for 3 min under 10kg/cm
2
pressure. Polymer uptake, density, modulus of rupture, and water absorption of samples were determined.
Results and Discussion
(i) The investigation provides strong evidence to the suitability and utilization of epoxidised diallyl phthalate
polymer as an additive to diallyl phthalate polymer based moulding composition. Data relating to mechanical
property improvements by substitution of DAPP polymer by EDAPP polymer have been found up to 20 per
cent. Above 20 per cent there is a declining trend which militates against the usage
(Tables 1-4). The electrical property is unaltered by substitution (Table 5).
Gel permeation chromotographic data of DAP polymer and EDAP polymer indicate absence of significant
reduction in molecular weight (Figure 1 and 2). Hence there is likelihood of parity in performance of the
derived moulding compositions. This view is further strengthened by rheological data of the moulding
compositions (Figure 3 and 4). The data presented together in a diagram exhibit virtual superimposition (Figure
5).
The thermogravimetry of the two compositions indicated the absence of any significant difference in thermal
resistance. DAP base moulding powder shows a weight loss of 42.7 per cent as a consequence of complete cycle
of heating upto 750oC. EDAP modified composition underwent 41.7 per cent weight loss. The absence of
change of decomposition point and near equality of percentage of weight loss confirm that partial substitution of
DAP polymer by EDAP polymer has no adverse impact on thermal stability (Figure 6 and 7).
J SCI IND RES VOL 63 APRIL 2004
368
A tentative view can be propounded relating to critical upper limit of 20 per cent and decline at
Table 1— Substitution of DAP polymer by EDAP polymer
Sl. No DAP polymer
content
per cent
EDAP
polymer
content
per cent
Modulus of
rupture
kg/cm2
1 100 619
2 80 20 725
3 60 40 541
4 40 60 668
5 20 80 393
6 0 100 299
Table 2—Compressive strength
100 per cent DAP 1400 kg/ cm2
80 per cent DAP + 20 per cent EDAP 1652 kg/ cm2
Table 3—Impact strength
100 per cent DAP 0.180
80 per cent DAP + 20 per cent EDAP 0.128
Table 4—Hardness
100 per cent DAP 115
80 per cent DAP + 20 per cent EDAP 124
Table 5 — Dielectric breakdown voltage and strength
Voltage Dielectric strength
kv kv/mm
100 per cent DAP 35 10
80 per cent DAP 35.6 10.86
+ 20 per cent EDAP
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
369
Figure 1 — Data relating to gel permeation chromatography of DAP powder
J SCI IND RES VOL 63 APRIL 2004
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Figure 2 — Data relating to gel permeation chromotograph of EDAP polymer
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
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Figure 3 — Rheological data of DAPP based moulding composition
J SCI IND RES VOL 63 APRIL 2004
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Figure 4 — Rheological data of moulding composition using 80 per cent DAPP and 20 per cent EDAPP
higher levels. Up to 20 per cent epoxidised DAPP may function as a compatibiliser reducing interfacial tension
and improvement of mechanical properties6. The absence of any serious reduction in molecular weight by
epoxidation is shown by GPC data fulfilling the basic requirement of molecular size.
The catalyst used in moulding is an acid generator
which interacts with the oxirane ring of EDAPP,
thereby generating vic-glycol moiety. Above 20 per
cent EDAPP may become a contender to DAPP for free
radicals causing imperfect or incomplete cure. Further
above 20 per cent the vic-glycol group may be cleaved
by free radicals, thereby causing chain scission and
resultant dimunition of molecular size impairing
efficiency as compatibiliser, since the optimal
molecular size is an essential requirement for action as
a compatibiliser. It may cause decrease in the cohesion
of composition. Thus the symbiotic action of decrease
in compatibiliser efficiency and catalyst inadequacy
accounts for the observed declining performance at
higher levels of substitution.
But crucial to the expansion of market is likely the
performance of the product under severe and harsh
conditions of environmental deterioration for appli-
cations in avionics, aerospace, satellite technology, and
submarine sectors. An accurate appraisal of
performance under stringent conditions of environ-
mental stress is sine qua non for the verdict on the value of the innovation.
(ii) Epoxy resins have acquired almost unchallenged
Figure 5 — The data presented in Figure 3 and Figure 4 presented
together to highlight the near equivalence
Figure 6 — Data relating to thermogravimetry of DAPP based composition
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
373
supremacy for nearly a century in the case of adhesives with usage in electrical and electronic sectors, oil wells,
satellites, roads and bridges, and
buildings constructions and supersonic aircraft. For the cost reduction and enhancement of performance reactive
diluents are used. It has been found that epoxidised diallyl phthalate polymer is an effective reactive diluent to
epoxy resin adhesives with prospects of usage with reduced cost.
The results confirm that epoxy resin and EDAP polymer – EDAP monomer combination is an attractive
composite adhesive for wood. Peak performance is indicated at extension levels of 20-40 per cent (Tables 6-11).
Further the samples laminated by the composite adhesive were not affected by water. Hence the glue system is
suitable for wood joinery work.
Work was extended to examine the suitability for production of decorative laminates using decorative veneer.
The unexpected rise in the price of decorative wood has necessitated the use of extremely thin veneer due to
cost deletion. The composite adhesive developed has an advantage of facile spreading on glue surface and
generates a bond unaffected by cold water. Penetration to the surface was not found. Therefore the composition
developed is attractive for use in manufacture of decorative laminates.
(iii) Environmental compulsions have stimulated search for renewable raw materials. The wood based
Table 6 —Formulations investigated
Composition
of adhesive
Epoxy resin
AW106
Hardner
HV953U
Reactive diluent
25 per cent
solution of
EDAPP in EDAP
monomer
1 100 80 0
2 80 80 20
3 60 80 40
Figure 7 — Data pertaining to thermogravimetry of constituted 80 per cent DAPP and 20 per cent EDAPP
J SCI IND RES VOL 63 APRIL 2004
374
4 40 80 60
5 20 80 80
6 0 80 100
Table 7 — Tests results of plywood made with commercial
epoxy resin
Failing load Wood failure
in kg per cent
388 15
262 50
354 70
340 60
440 80
Table 8—Adhesive composition
Epoxy resin 100 per cent
Reactive diluent – EDAP mix at 20 per cent
Failing load, kg Wood
failure per cent
153 45
170 20
163 100
150 15
187 30
Table 9 — Adhesive composition
Epoxy resin 100
EDAP monomer
polymer mix 20
Failing load, kg Per cent
wood failure
205 80
185 80
195 100
162 15
150 50
industry is therefore engaged in the process of substitution of resources from natural forests by raw materials
from regenerative plantations. Wood polymer composites have therefore emerged as an attractive option in
materials. Both thermoplastic and thermosetting polymers have been used to produce composites. Earlier
investigations used phenolic resins and the composite was known as lignostone7. Acrylic and vinyl compounds
were later deployed and the reaction was induced by heat and / or catalyst8. The availability of γ-ray source
enlarged the scope
of action by the capability for radiation polymerization.
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
375
Wood polymer composites improved mechanical properties in conjunction with enhanced resistance to water
and resistance to fungal and insect attack9. Upgradation of the quality of wood by diverse chemical systems
acquired importance and several novel procedures have been developed10
. Chemical modification of hardboard
using DAP polymer was therefore undertaken for developing a versatile and durable fibreboard possessing
resistance to environmental degeneration.
Table 10—Adhesive composition
Epoxy resin 100
EDAPP + EDAP monomer 40
Failing load kg Per cent
wood failure
153 45
170 20
163 100
150 15
187 30
Table 11—Results for solid wood
Epoxy resin 100
EDAPP mix 20 per cent
Failing load kg Per cent
wood failure
150 0
222 0
300 0
The test samples were kept immersed in cold water for 8 h. No delamination was found to occur.
The processing has resulted in significant improvement of mechanical properties with reduction in water
absorption. The product parameters surpass IS standard requirements for superior quality hardboard namely,
tempered hardboard. Tempered hardboard is manufactured by treatment of hot hardboard from the press with
drying oil to give a retention of 8 per cent by weight. The drying oil undergoes oxidative polymerization with
concurrent side reactions like, cyclisation, copolymerisation with oxygen, branching, and even Diels-Alder
reaction. The complexity of these processes endows the resulting polymer with structural irregularities
vulnerable to the onset of degradation processes (Figure 8). Hardboard, modified by DAP polymer is less prone
to degradation because of the deficiency of defective sites (Tables 12-15).
It has been established that lignocellulose possesses ethylenic linkages. These linkages can undergo
crosslinking reaction with the double bonds in DAP polymer activated by the free radicals generated by the
decomposition of catalyst. The resultant product comprising two structurally different polymer chains
J SCI IND RES VOL 63 APRIL 2004
376
Figure 8 — Data showing the dependent uptake of DAPP from solution by hardboard
Table 12—Uptake of DAP polymer from solution by hardboard
Weight of sample (g) Per cent
polymer uptake
30.47 5.3
30.76 5.36
31.1 5.31
36.16 5.31
36.16 5.32
Table 13 – Properties of hardboard modified by DAP polymer
Density Modulus of Water absorption
g/cc rupture kg/cm2 per cent in 24 h
0.86 367 40.30
0.861 417 30.4
0.862 395 32.1
0.863 402 32.17
0.863 480 34
with cross-links resembles ladder polymer having chain-stiffening without segmental motion. Degradation of
such a macromolecule requires simultaneous rupture of several bonds with large energy requirements.
Hence, it may be mentioned that hardboard modified by DAPP surpasses tempered hardboard in durability
due to the advantages of the polymeric structure. This speculative view has to be buttressed by conclusion
from environmental impact studies.
Table 14 —Properties after thermal processing
Wt of Wt after Density MOR Water
sample absorption g/cc kg/cm2 absorption
(g) (g) in 24h
per cent
MENON & SELVARAJ: ADVANCES IN APPLIED CHEMISTRY OF ALLYLIC POLYMERS
377
30.45 33.42 0.95 795 20.16
30.61 33.22 0.946 754 18.20
30.31 32.84 0.95 755 18.37
30.33 32.9 0.945 700 19.86
30.26 33 0.95 788 20.70
Equilibrium moisture content 5.6 per cent
IS Specification for tempered hardboard
MOR kg/cm2 ≥ 500
Water absorption in 24 h ≤ 20 per cent
Table 15 — Electrical properties
Thickness Break down Dielectric
voltage strength
2.95 mm 7.5 kv 2.54 kv/mm
3. mm 7.5 kv 2.5 kv/mm
2.95 mm 7.5 kv 2.54 kv/mm
3.1 mm 7.5 kv 2.54 kv/mm
Prospective applications of the product in building industry encompass cladding, box beams, ceilings,
roofing, partitions, etc. Housing for instrument in environmentally aggressive industrial locations, containers,
and luggage are some of the possible opportunities. Application in electrical industry as substitute for Compreg
in selected sectors may also emerge due to attractive properties (Tables 15).
References
1 Gewariker R, Viswanathan N V & Sreedhar J, Polymer science (Wiley-Eastern, New Delhi) 1986, p22.
2 Simpson W, Hot T & Zetie R J, Polym Sci, 10 (1953) 489.
3 Ravve A, Organic chemistry of macromolecules (Marcel-Dekker Inc, New York) 1967, p80.
4 Harry Szmant H, Organic building blocks of chemical industry (John Wiley and Sons, New York) 1989, p.255.
5 Selvaraj A, Investigation in the applied chemistry of diallyl phthalate polymer and its epoxidised derivative, MSc (Applied
Chemistry) Thesis, Bharathiar University, 1998, Coimbatore.
6 Oksman K, Wood Sci Technol, 30 (1996) 197.
7 Mayer J A & Skar C, Forest Prod J, 16(5) (1966) p426.
8 Mayer J A, Wood Sci, 14 (1981) 2.
9 Desch H E & Dinwoodie J M, Timber structure, properties, conversion and use (Macmillan Press Ltd, London) 1996, pp212.
10 Menon C C, J Sci Ind Res, 61 (2002) 444.
*Author for correspondence