Styrene butadiene block copolymers for film applications
View Patent ↗We disclose a monovinylarene-conjugated diene block copolymer containing a plurality of monovinylarene-conjugated diene mixed blocks, wherein each mixed block contains conjugated diene units and monovinylarene units in a weight ratio of about 0.05 to about 0.33. We also disclose a composition containing (a) from about 50 parts by weight to about 95 parts by weight of the monovinylarene-conjugated diene block copolymer and (b) from about 5 parts by weight to about 50 parts by weight of polystyrene; wherein the monovinylarene-conjugated diene block copolymer and the polystyrene total 100 parts by weight. We further disclose a method of shrink-wrapping an object or a group of objects by wrapping the object or the group of objects with a film containing the composition, to yield a wrapped object or group of objects, and heating the wrapped object or group of objects to a temperature and for a duration sufficient to shrink the film in at least a first direction, to yield a shrink-wrapped object or group of objects.
1. A method of forming a monovinylarene-conjugated diene block copolymer, the method comprising:
polymerizing a monovinylarene and a conjugated diene in a mixture comprising a diluent;
adding as separate additions a first coupling agent and a second coupling agent to the mixture,
wherein the monovinylarene-conjugated diene block copolymer formed comprises:
a proximal conjugated diene block comprising from about 5 phm conjugated diene units to about 50 phm conjugated diene units; and
a plurality of monovinylarene-conjugated diene mixed blocks, wherein each monovinylarene-conjugated diene mixed block contains conjugated diene units and monovinylarene units with a weight ratio of conjugated diene units to monovinylarene units of about 0.05 to about 0.33.
2. The method of claim 1 , wherein the first coupling agent and the second coupling agent comprise the same compound.
3. The method of claim 1 , wherein the monovinylarene-conjugated diene block copolymer formed comprises at least three monovinylarene-conjugated diene mixed blocks.
4. The method of claim 1 , wherein the monovinylarene-conjugated diene block copolymer formed comprises at least four consecutive monovinylarene-conjugated diene mixed blocks.
5. The method of claim 1 , comprising polymerizing the monovinylarene to form a distal monovinylarene block of the monovinylarene-conjugated diene block copolymer.
6. The method of claim 1 , comprising polymerizing the conjugated diene to form the proximal conjugated diene block of the monovinylarene-conjugated diene block copolymer.
7. The method of claim 1 , comprising forming a blend, wherein the blend comprises the monovinylarene-conjugated diene block copolymer and polystyrene.