Polymer Degradation and Stability
Volume 95, Issue 3,
, Pages 353-362
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Two reactive comonomers, divinyl benzene (DVB) and trimethylolpropane triacrylate (TRIS), were evaluated for their role in effecting the melt free radical grafting reaction of the monomer glycidyl methacrylate (GMA) onto polypropylene (PP). The characteristics of the GMA-grafting systems in the presence and absence of DVB or TRIS were examined and compared in terms of the yield of the grafting reaction and the extent of the main side reactions, namely homopolymerisation of GMA (poly-GMA) and polymer degradation, using different chemical compositions of the reactive systems and processing conditions. In the absence of the comonomers, i.e. in a conventional system, high initiator concentrations of peroxides were typically required to achieve the highest possible GMA grafting levels which were found to be generally low. Concomitantly, both poly-GMA and degradation of the polymer by chain scission takes place with increasing initiator amounts. On the other hand, the presence of a small amount of the comonomers, DVB or Tris, in the GMA-grafting system, was shown to bring about a significant increase in the grafting level paralleled by a large reduction in poly-GMA and PP degradation. In the presence of these highly reactive comonomers, the optimum grafting system requires a much lower concentration of the peroxide initiator and, consequently, would lead to the much lower degree of polymer degradation observed in these systems. The differences in the effects of the presence of DVB and that of TRIS in the grafting systems on the rate of the GMA-grafting and homopolymerisation reactions, and the extent of PP degradation (through melt flow changes), were compared and contrasted with a conventional GMA-grafting system.
In-situ melt grafting reactions of polar functional groups on commercial inert hydrocarbon polymers such as polyolefins and their copolymers has been the subject of intense studies over the last three decades with the aim of producing a new range of specialty materials with targeted properties . Polypropylene, PP, benefits from its low cost and versatile set of properties hence its use in many commercial applications. However, it is an inert hydrocarbon polymer that lacks the presence of reactive functionality and this limits its application in many technologically important fields due to, for example, its low surface energy, poor dyeability and compatibility with polar polymers. Various reactive (vinyl-based) modifiers have therefore been employed to functionalise PP to introduce new properties that would expand its uses in new areas of applications such as in compatibilisation of polymer blends, interfacial coupling to polymers and inorganic substrates, crosslinking and reactive stabilisation , , , , .
Most attention has been given to free radical melt grafting on PP of two such vinyl-based monomers, maleic anhydride, MA, and glycidyl methacrylate, GMA. These monomers are bifunctional monomers containing an unsaturated function capable of free radical grafting on hydrocarbon polymers and a highly electrophilic moiety that can react with different nucleophilic functions such as carboxylic, hydroxide and amine groups, and this in turn can then be used to promote further reactions, e.g. reactive compatibilisation in blends and alloys . The grafting efficiency of both GMA and MA on different hydrocarbon polymers, however, has been shown to be generally low , , , , . In the case of GMA, this is mainly due to its low reactivity towards macroradicals and high tendency towards homopolymer formation.
In our laboratory, we have developed a highly effective and versatile functionalisation strategy that is capable of improving the grafting efficiency of variety of functional monomers on polymers. This approach is achieved through in-situ co-grafting of a small amount of a more reactive (compared to the modifier) comonomer (co-agent) , , , , , . In earlier work, we have reported the use of the polyfunctional comonomer, trimethylolpropane triacrylate, TRIS, with different reactive modifiers, e.g. with GMA in EPR  and with various reactive antioxidants in PP , , , and have shown that these systems give rise to a dramatic increase in the level of grafting of the modifiers on the polymers examined.
We report here our work on the effect of two reactive comonomers, a bifunctional one, divinyl benzene, DVB, and a tri-functional one, TRIS on the characteristics of free radical melt grafting reactions of GMA on PP and to compare these grafting reactions with similar ones but which are carried out in the absence of a comonomer (conventional system).
Granules of polypropylene Apryl-3020 BNI (PP) with melt flow rate of 2.0g/min (at 230°C/2.16kg) were kindly supplied by Elf-Atochem. GMA (97% purity), DVB and TRIS were used as received from Aldrich Chemical Co. The peroxides used were 2,5-dimethyl-2, 5-bis(t-butyl peroxy) hexane (Trigonox 101, T101), 1,1-di(tert-butylperoxy)-3,3,5-trimethyl cyclohexane (Trigonox T-29B90) were kindly donated by Akzo Nobel, dicumyl peroxide (DCP) and benzoyl peroxide (BPO) were purchased from Aldrich and
Conventional PP-GMA grafting system in absence of comonomer
In a conventional peroxide-initiated GMA-PP grafting system (i.e. in absence of a comonomer), in addition to the target grafting reaction, there is typically at least two other competing side reactions involving GMA-homopolymer formation (poly-GMA) and degradation of PP mainly by chain scission, reaction (1).
The peroxide (Trigonox 101)-initiated GMA-PP conventional melt grafting system was examined at different peroxide and initial GMA concentrations and at different processing temperatures.
The incorporation of a small concentration of the highly reactive comonomers DVB or TRIS in PP/GMA free radical melt grafting system has been shown to bring about advantageous changes in the grafting yield of GMA. In the presence of a very small concentration of peroxide a faster rate of grafting is achieved concomitant with a substantial reduction in the main competing side reactions, namely chain scission or comonomer-assisted crosslinking of the polymer and the GMA-homopolymerisation (a
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N-vinyl pyrrolidone-assisted free radical functionalization of glycidyl methacrylate onto styrene-b-(ethylene-co-butylene)-b-styrene
2010, Reactive and Functional Polymers
Citation Excerpt :
During the processing procedure, however, side reactions including homopolymerization of the functional monomer, degradation, and cross-linking of the matrix polymer will occur , resulting in low GE. To improve the GD and GE, the ternary radical grafting system has been developed by introducing a reactive co-agent, such as styrene (St) [9–12], trimethylolpropane triacrylate , or divinyl benzene [13,14], to the classical binary system consisting of the initiator and the functional monomer. In particular, St is widely used as co-agent due to its superiority in increasing GE while minimizing the degradation of polymer [10–12].
N-vinyl pyrrolidone (NVP)-assisted free radical functionalization of glycidyl methacrylate (GMA) onto styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) was investigated to attempt to overcome the low grafting reactivity of GMA and the low efficiency of the styrene (St)-assisted functionalization method. By using the optimal amount of NVP, the degree of GMA grafting was increased by at least 7.5 and 2.5-fold when compared to GMA alone and the St-assisted grafting procedure, respectively. Also, no apparent cross-linking or degradation reactions of SEBS were observed. It was proposed that NVP reacted first with SEBS macroradicals, and then the resulting NVP-macroradicals copolymerized with GMA to produce high degrees of grafting of both GMA and NVP onto SEBS.See AlsoPathomechanisms of epidermolysis bullosa: Beyond structural proteinsIntercalated water-induced hysteretic friction behavior of graphene, h-BN, and MoS2Plasmon coupling using eigenmode expansion and its sensing applicationsCells | Free Full-Text | Tortuous Cardiac Intercalated Discs Modulate Ephaptic Coupling
Addition of divinyl benzene comonomer to glycidyl methacrylate grafting to cyclic natural rubber
2021, IOP Conference Series: Earth and Environmental Science
Improvements in the synthesis and characterization of glycidyl methacrylate-grafted EPDM through melt free-radical process
2020, Rubber Chemistry and Technology
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