Versatile Approach for Preparing PVC-Based Mikto-Arm Star Additives Based on RAFT Polymerization

Abstract

A versatile approach to the synthesis of migration-resistant poly­(vinyl chloride) (PVC) additives is described and a preliminary assessment of their properties is presented. The process involves the synthesis of AB2 3-mikto-arm stars, star-[PVC-block-(polyB);(polyB)2] or star-[PVC;(polyB)2], that contain a reversible addition-fragmentation chain transfer (RAFT)-synthesized PVC segment, to provide compatibility with PVC and good migration resistance, and multiple RAFT-synthesized segments (polyB), where polyB is based on more activated monomer (a styrene or a methacrylate) that contains the functionality required to impart the desired additive properties. The approach to PVC-based stars comprises three steps: (a) synthesis of a hydroxy-functional PVC [X-PVC­(OH) n ] by RAFT polymerization mediated by a hydroxy-functional xanthate [X-(OH) n ], (b) conversion of the X-PVC­(OH) n to the corresponding trithiocarbonate, X-PVC-(CDTPA) n , by the Steglich esterification with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)­sulfanyl]­pentanoic acid (CDTPA), and (c) formation of star polymer additives by RAFT polymerization mediated by X-PVC-(CDTPA) n . The stars prepared include a plasticizer (B = butyl acrylate), a reactive dispersant for use in forming silica nanocomposites (B = 3-methacryloxypropyltrimethoxysilane), UV stabilizers (B = 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]­ethyl methacrylate or 2-hydroxy-4-acryloxybenzophenone), and flame retardants (B = 4-vinylbenzyl phosphonate or (diethoxyphosphoryl)­methyl methacrylate). Although much optimization remains to be done, our preliminary study shows that the synthesized mikto-arm star additives can be effective in imparting the anticipated properties to PVC.

“All-PVC” Flexible Poly(vinyl Chloride): Nonmigratory Star-Poly(vinyl Chloride) as Plasticizers for PVC by RAFT Polymerization

“…RAFT-3 ( 3a ) and RAFT-4 ( 3b ) were used to prepare a series of three- and four-arm star -PVC (Table ) using conditions similar to those in our previous work on xanthate-mediated polymerization of VC. , We denote M n < 2000 as low M n PVC (PVC-1), 2000 < M n < 5000 as middle M n PVC (PVC-2), and M n > 5000 as high M n PVC (PVC-3) in the following text. A low M n linear PVC was also prepared using the mono-xanthate, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)­propanoate (HECP), to facilitate a comparison of properties with those of the three and four-arm star -PVC.…”

“…For the stars, there is also a trend for thermal stability to increase with molar mass. This might be attributed to a lower concentration of defect structures in RAFT-synthesized PVC compared to conventionally prepared PVC. , …”

“…We and others have investigated block copolymers and mikto-arm star copolymers comprising PVC blocks, such as poly­(vinyl chloride)- block -polycaprolactone (PVC- b -PCL) or poly­(vinyl chloride)- block -poly­(butyl acrylate) (PVC- b -PBA), as internal plasticizers. − In these structures, as with the PVC-based internal plasticizers mentioned above, the PVC segments both ensure compatibility with PVC and impart improved migration resistance. This knowledge prompted us to investigate star -PVC as a potential non-migratory plasticizer in an “all PVC” flexible PVC.…”

“…However, there appear to be no published data for the 4- star -[PBA- block -PVC], or the 4- star -PVC, in this application. We recently reported on the RAFT synthesis of mikto-arm star polymers of general structure star -[PVC- block -(polyB); (polyB) 2 ] or star -[PVC; (polyB) 2 ], wherein the PVC arm imparts resistance to migration and the polyB segments impart performance as a plasticizer (B = butyl acrylate), a reactive dispersant for use in forming silica nanocomposites (B = 3-methacryloxypropyltrimethoxysilane), UV stabilizers (B = 2-[3-(2 H -benzotriazol-2-yl)-4-hydroxyphenyl]­ethyl methacrylate or 2-hydroxy-4-acryloxybenzophenone), or flame retardants [B = 4-vinylbenzyl phosphonate or (diethoxyphosphoryl)­methyl methacrylate] …”

Fundamentals of reversible addition–fragmentation chain transfer (RAFT)

“…These are star polymers prepared by RAFT polymerization that impart long term, temperature independent, viscosity to fluids such as oils (Brzytwa & Johnson, 2011). A further example is the preparation of novel RAFT synthesized additives that enable production of flexible PVC that is free of migratory additives and plasticizers (Sun, Choi, Feng, Moad, & Thang, 2019;Sun et al, 2020).…”