Splice to repair damaged 100A aluminum feeder
You'll need a pretty chunky box for those splices

Wires 4AWG and up can't be spliced in any old junction box as they're simply too stiff and fat to fit into junction-box-sized boxes.  Instead, you need to use what's called a pull box in the trade to house your splicing job, which invokes the box sizing rules in NEC 314.28(A), specifically (A)(2):


  (A) Minimum Size. For raceways containing conductors of
  4 AWG or larger that are required to be insulated, and for
  cables containing conductors of 4 AWG or larger, the minimum
  dimensions of pull or junction boxes installed in a raceway or
  cable run shall comply with 314.28(A)(1) through (A)(3).
  Where an enclosure dimension is to be calculated based on the
  diameter of entering raceways, the diameter shall be the metric
  designator (trade size) expressed in the units of measurement
  employed.
  
  (2) Angle or U Pulls, or Splices. Where splices or where angle
  or U pulls are made, the distance between each raceway entry
  inside the box or conduit body and the opposite wall of the
  box or conduit body shall not be less than six times the metric
  designator (trade size) of the largest raceway in a row. This
  distance shall be increased for additional entries by the amount
  of the sum of the diameters of all other raceway entries in the
  same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used.
  
  Exception: Where a raceway or cable entry is in the wall of a box or
  conduit body opposite a removable cover, the distance from that wall to
  the cover shall be permitted to comply with the distance required for one
  wire per terminal in Table 312.6(A).
  
  The distance between raceway entries enclosing the same
  conductor shall not be less than six times the metric designator
  (trade size) of the larger raceway.
  
  When transposing cable size into raceway size in
  314.28(A)(1) and (A)(2), the minimum metric designator
  (trade size) raceway required for the number and size of
  conductors in the cable shall be used.


As a result of this, we come up with 477mm2 for a 1-1-1-3 aluminum SER cable at slightly under 1" diameter, which fits into a 1.5" conduit (it's slightly too large for a 1.25" conduit).  So, we'll need an 10" by 10" by 4", NEMA 1 (indoor rated), screw cover pull box (the Wiegmann SC101004 should do the trick), along with a matching flushmount cover (Wiegmann SCF1010), and cable entrance fittings that can work with such a large cable.  The Polaris connectors you have chosen will work fine for splicing, by the way: the only caveat with them is that you'll need to use an inch-pound torque wrench to tighten them to their specification torque for a reliable connection (this is required by 110.14(D) of the 2017 NEC).